Mems steering mirrors for applications in photonic integrated circuits

ABSTRACT

An integrated optical assembly includes an optics mount. The optics mount has disposed thereon a light source for providing a beam of light and a lens configured to focus the beam of light. The integrated optical assembly includes a photonic integrated circuit (PIC) mechanically coupled to the optics mount. The PIC has disposed thereon a grating coupler for receiving the beam of light and coupling the beam of light into a waveguide. The integrated optical assembly includes a microelectromechanical systems (MEMS) mirror configured to receive the beam of light from the lens and redirect it towards the grating coupler. A position of a reflective portion of the MEMS mirror is adjustable to affect an angle of incidence of the beam of light on the grating coupler.

RELATED APPLICATIONS

The present application is a continuation of, and claims the benefit ofand priority to, U.S. patent application Ser. No. 15/634,632, titled“MEMS STEERING MIRRORS FOR APPLICATIONS IN PHOTONIC INTEGRATEDCIRCUITS,” filed Jun. 27, 2017, which claims the benefit of and priorityto U.S. Provisional Patent Application No. 62/512,626, titled “MEMSSTEERING MIRRORS FOR APPLICATIONS IN PHOTONIC INTEGRATED CIRCUITS,”filed on May 30, 2017, the entire contents of each of which are herebyincorporated by reference for all purposes.

BACKGROUND

Optical communications use modulated light beams to convey informationthrough optical fibers, free space, or waveguides. A beam of light canbe modulated either directly by modulating current to a light source, orexternally by using an optical modulator to modulate a continuous-wavelight beam produced by the light source. External modulation hasadvantages in that it can handle higher power and frequencies; however,the required components can be larger, more complex, and more expensive.

SUMMARY

At least one aspect is directed to an integrated optical assembly. Theintegrated optical assembly includes an optics mount having disposedthereon a light source for providing a beam of light and a lensconfigured to focus the beam of light. The integrated optical assemblyincludes a photonic integrated circuit (PIC) mechanically coupled to theoptics mount and having disposed thereon a grating coupler for receivingthe beam of light and coupling the beam of light into a waveguide. Theintegrated optical assembly includes a microelectromechanical systems(MEMS) mirror configured to receive the beam of light from the lens andredirect it towards the grating coupler. A position of a reflectiveportion of the MEMS mirror is adjustable to affect an angle of incidenceof the beam of light on the grating coupler.

In some implementations, the grating coupler includes silicon.

In some implementations, the optics mount includes silicon with ananti-reflective coating on at least one surface.

In some implementations, the light source is a distributed feedbacklaser. In some implementations, the integrated optical assembly caninclude an optical isolator disposed on the optics mount and configuredto receive the beam of light from the lens and pass it in a firstdirection towards the MEMS mirror while preventing light from passingthrough it in a second direction opposite the first direction.

In some implementations, the integrated optical assembly can include amonitor photodiode disposed on the PIC for measuring an amplitude oflight coupled into the waveguide.

In some implementations, the MEMS mirror is movable to adjust the angleof incidence from zero degrees from normal to a light-receiving surfaceof the grating coupler, to 20 degrees from normal.

In some implementations, the integrated optical assembly has dimensionssuitable for inclusion in an optical transceiver device.

In some implementations, the MEMS mirror can rotate in two dimensions.

In some implementations, the MEMS mirror includes an actuator foradjusting the position of the reflective portion.

In some implementations, the MEMS mirror is configured to be continuallyor periodically repositioned throughout a service life of the integratedoptical assembly.

At least one aspect is directed to an optical communications system. Theoptical communications system includes an optics mount having disposedthereon a light source for providing beam of light and a lens configuredto focus the beam of light. The optical communications system includes aphotonic integrated circuit (PIC) mechanically coupled to the opticsmount. The PIC has disposed thereon a grating coupler for receiving thebeam of light and coupling the beam of light into a waveguide, and amonitor photodiode for measuring an amplitude of light coupled into thewaveguide. The optical communications system includes amicroelectromechanical systems (MEMS) mirror configured to receive thebeam of light from the lens and redirect it towards the grating coupler.A position of a reflective portion of the MEMS mirror is adjustable toaffect an angle of incidence of the beam of light on the gratingcoupler. The optical communications system includes a controllerconfigured to receive an indication of the amplitude of the lightcoupled into the waveguide and control the position of the MEMS mirrorto increase the indication of the amplitude.

At least one aspect is directed to a method of manufacturing anintegrated optical assembly. The method includes providing an opticsmount having disposed thereon a light source for providing beam of lightand a lens configured to focus the beam of light. The method includesproviding a photonic integrated circuit (PIC) having disposed thereon agrating coupler for receiving the beam of light and coupling the beam oflight into a waveguide. The method includes providing amicroelectromechanical systems (MEMS) mirror configured to receive thebeam of light from the lens and redirect it towards the grating coupler.A position of a reflective portion of the MEMS mirror is adjustable toaffect an angle of incidence of the beam of light on the gratingcoupler. The method includes assembling the optics mount, the MEMSmirror, and the PIC into the integrated optical assembly.

In some implementations, the method can include providing a modulator onthe PIC for modulating light coupled into the waveguide.

In some implementations, the method can include providing a monitorphotodiode on the PIC; and measuring, using the monitor photodiode, anamplitude of light coupled into the waveguide. In some implementations,the method can include calibrating the position of the MEMS mirror toincrease coupling of the beam of light into the waveguide.

These and other aspects and implementations are discussed in detailbelow. The foregoing information and the following detailed descriptioninclude illustrative examples of various aspects and implementations,and provide an overview or framework for understanding the nature andcharacter of the claimed aspects and implementations. The drawingsprovide illustration and a further understanding of the various aspectsand implementations, and are incorporated in and constitute a part ofthis specification.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are not intended to be drawn to scale. Likereference numbers and designations in the various drawings indicate likeelements. For purposes of clarity, not every component may be labeled inevery drawing. In the drawings:

FIG. 1A is a graph of an example relationship of loss versus wavelengthfor coupling light into an optical grating coupler;

FIG. 1B is a graph of example relationships of loss versus wavelengthfor coupling light into three different optical grating couplers;

FIG. 2 is a graph of an example relationship of optimum wavelengthversus angle of incidence for coupling light into an optical gratingcoupler;

FIG. 3 is a block diagram of an integrated optical assembly, accordingto an illustrative implementation;

FIG. 4 is a block diagram of a photonic integrated circuit (PIC) for usein an integrated optical assembly, according to an illustrativeimplementation;

FIG. 5A is a diagram of a two-axis microelectromechanical system (MEMS)mirror assembly for use in an integrated optical assembly, according toan illustrative implementation;

FIG. 5B is a diagram of a single-axis microelectromechanical system(MEMS) mirror assembly for use in an integrated optical assembly,according to an illustrative implementation; and

FIG. 6 is a flowchart of an example method of manufacturing anintegrated optical assembly, according to an illustrativeimplementation.

DETAILED DESCRIPTION

This disclosure generally relates to an integrated optical assembly forcoupling a beam of light into a photonic integrated circuit (PIC) usingan adjustable mirror. The assembly can include the laser light source,optical components such as a lens and an optical isolator, the mirror,and a PIC having an optical grating coupler for coupling the laser intothe PIC. The PIC can include a waveguide to receive the light from thegrating coupler. The PIC can additionally include power splitters,monitor photodiodes, and a modulator for modulating the light.

A grating coupler is an optical device that can couple light travelingin free space or an optical fiber into a waveguide (or vice-versa). Thegrating coupler is a diffractive element with a limited opticalbandwidth over which it can efficiently couple light into or out of thewaveguide. Furthermore, optical grating couplers with large mode fielddiameters may have even narrower bandwidths. Process variations in thefabrication of the grating coupler can result in variation of the centerwavelength from one grating coupler to another. In addition, the angleof incidence of light impinging on the grating coupler also affects thecenter wavelength; e.g., a steeper angle of incidence may result in ashorter center wavelength. Process variations in the assembly can alsoaffect the angle of incidence of light on the grating coupler. Suchprocess variations can include, for example and without limitation,position of the light source, lens, mirror, and grating coupler. Inaddition, the wavelength of light generated by the light source itselfmay vary. For example and without limitation, optical communicationsystems using wavelength-division multiplexing may employ wavelengthsranging from 1260 to 1340 nm.

An integrated optical assembly can compensate for the variations inprocesses and light wavelength by taking advantage of the relationshipbetween center wavelength of the grating coupler and the angle ofincidence of light impinging on the grating coupler. For example,instead of a fixed reflector such as a prism, mirror, or polished fibertip, the integrated optical assembly can include an adjustable mirrorfor redirecting the laser onto the grating coupler. The adjustablemirror can be a microelectromechanical system (MEMS) mirror that can beadjusted using, for example, electrostatic actuators controlled by acontroller using feedback from a monitor photodiode on the PIC. In someimplementations, the mirror can include other small form-factor mirrors;for example, the mirror can include a reflective surface glued orotherwise affixed to one or more laser-cut sheet metal shims. In someimplementations, the mirror can remain free to move for the service lifeof the assembly such that future adjustments can be made.

Use of a MEMS mirror allows for miniaturization of the integratedoptical assembly. The size of the entire integrated optical assembly canbe on the order of a few millimeters in its longest dimension. This canmake the integrated optical assembly appropriate for use in, forexample, a data communications transceiver. In addition, the presence ofthe MEMS mirror allows the other components to be fixed to each other ina mass production environment, with alignment adjustments to be madeusing the mirror. This allows for a simpler fabrication process withwider tolerances, which can reduce the overall cost of the device.

FIG. 1A is a graph 100 of an example relationship of loss versuswavelength for light coupling into an optical grating coupler. Opticalgrating couplers can be used to couple light traveling in free space oran optical fiber into a waveguide, and vice-versa. Optical gratingcouplers are therefore useful in optical communications for couplinglight into and out of photonic integrated circuits (PICs) in opticaltransmitters, receivers, and transceivers. An optical grating couplermay include surface features such as lines or ridges that create aninterface suitable for receiving or emitting an optical signal. Such anoptical grating coupler is a resonant device; therefore, it will coupleoptical signals of a certain bandwidth around a center wavelength. Thecenter wavelength and bandwidth are functions of the dimensions of thesurface features of the optical grating coupler.

The graph 100 illustrates an example relationship of loss versuswavelength for coupling light into an optical grating coupler. Thewavelength at which the grating coupler is most efficient—i.e., leastlossy—is referred to as the center wavelength. The grating coupler cancouple light with a reasonable efficiency across a finite bandwidth (BW)around the center wavelength. The bandwidth can be defined as a range ofwavelengths of light over which coupling loss is less than, for example,1 dB, 3 dB, or 6 dB greater than the coupling loss at the centerwavelength.

FIG. 1B is a graph 150 of example relationships of loss versuswavelength for coupling light into three different optical gratingcouplers. Because optical grating couplers are resonant devices with acenter wavelength that depends on its surface features, processvariations in the fabrication of optical grating couplers can result invariation of the center wavelength from one optical grating coupler toanother. The graph 150 illustrates example relationships of loss versuswavelength for optical grating couplers 1, 2, and 3. For example,grating coupler 1 has a center wavelength 1, grating coupler 2 has acenter wavelength 2, and grating coupler 3 has a center wavelength 3.Thus, even though optical grating couplers may be manufactured for aparticular wavelength, process variation can result in optical gratingcouplers having center wavelengths that vary from the desiredwavelength. For example, the pitch or spacing of the surface featurescan affect the resonant behavior of the optical grating coupler, andthus the center wavelength. Without a way to compensate for the centerwavelength variation among optical grating couplers, the devicesemploying them may not operate as efficiently as they could.

FIG. 2 is a graph 200 of an example relationship of optimum wavelengthversus angle of incidence for coupling light into an optical gratingcoupler. The graph 200 shows that the center wavelength for optimumcoupling of light into an optical grating coupler can vary based on theangle of incidence. For example, at an angle of incidence of 5 degreesfrom normal to the surface of the optical grating coupler, the optimum(center) wavelength for efficient coupling of light will beapproximately 1325 nm. At an angle of incidence of 15 degrees, theoptimum wavelength will be approximately 1235 nm. This relationshipbetween angle of incidence and center wavelength can lead to anadditional source of variation in center wavelength among devices. Forexample, the relative positioning of the optical grating coupler, lightsource, lens, and mirror can affect the angle of incidence, and thus thecenter wavelength of the system. Slight variations in the alignment ofthe lens from device to device can result in variations in the angle ofincidence of the beams of light on the respective optical gratingcouplers. The variation in the angle of incidence among devices should,all things being equal, result in a corresponding variation in thecenter wavelength of each device, even though each device ismanufactured to operate at the same center wavelength.

The graph 200 shows, however, that the relationship between the angle ofincidence and the optimum wavelength behaves substantially linearly.This relationship can therefore be exploited to adjust the angle ofincidence and potentially compensate for variations in grating couplersurface features and the relative positions of system components. Forexample, the system can include a moveable mirror or reflector. Themirror angle can be adjusted to set the angle of incidence of lightimpinging on the grating coupler. The mirror angle can therefore beadjusted to set the angle of incidence in a manner that tunes the centerwavelength of the system to the desired wavelength. For example, in someimplementations, the wavelength of the light beam is 1310 nm. Using theexample measurements in the graph 200, the center wavelength of thesystem can be set to 1310 nm by adjusting the mirror such that the angleof incidence of light on the optical grating coupler is roughly 7degrees. The exact angle of incidence for efficient coupling of lightinto the optical grating coupler may depend on the dimensions of thegrating coupler surface features. Similarly, the mirror angle to achievethe desired angle of incidence may depend on the relative position ofother components of the integrated optical assembly. In both cases, theangle of the mirror can be used to optimize the angle of incidence forefficient coupling at the center wavelength. The graph 200 representsjust one example of a relationship between angle of incidence andoptimum wavelength. Other grating couplers will exhibit differentrelationships depending on their geometry and physical properties.

FIG. 3 is a block diagram of an integrated optical assembly 300,according to illustrative implementations. The assembly 300 includes anoptics mount 305 and a photonic integrated circuit (PIC) 310. The opticsmount 305 has disposed thereon a light source 315, a lens 320, and, insome implementations, an optical isolator 325. The PIC 310 includes anoptical grating coupler 330. The assembly 300 includes amicroelectromechanical system (MEMS) mirror 335 mounted to either orboth of the optics mount 305 and the PIC 310. The integrated opticsassembly 300 can function as an externally modulated laser, providing amodulated optical signal 365. A controller 370 can execute certainoperations of the integrated optical assembly 300 such as controlling aposition of a reflective portion of the mirror 335. For example andwithout limitation, the controller 370 can be used to adjust or optimizelight coupling over the lifetime of the device, including adjusting tocompensate for thermal expansion or contraction of components of theintegrated optical assembly 300.

In some implementations, the optics mount 305 can include silicon or befabricated from one or more silicon blocks or wafers. In someimplementations, the optics mount 305 can include an antireflective (AR)coating 340 on a top and/or bottom side in regions passing a light beam360. The AR coating can include a multi-layer hard oxide coating thatincludes silicon dioxide (SiO2) and hafnium dioxide (HfO2). The lightsource 315 can be mounted to the optics mount 305 with solder 345; forexample, gold/tin solder. The lens 320 and optical isolator 325 can bemounted to the optics mount 305 with a layer of epoxy 350. The opticsmount 305 can itself be mounted to the PIC 310 with a layer of epoxy355. The epoxy can be of a type having high transparency. For example,in some implementations, the epoxy can be a UV-curable optical path linkup epoxy.

In some implementations, the optics mount 305 can be betweenapproximately 2.5 mm and 5 mm long. In some implementations, the opticsmount 305 can be approximately 3.5 mm long. In some implementations, theoptics mount 305 can be between approximately 0.5 mm to 1.25 mm wide. Insome implementations, the optics mount 305 can be approximately 0.75 mmwide. In some implementations, the optics mount 305 can be betweenapproximately 0.5 mm to 1.5 mm tall. In some implementations, the opticsmount 305 can be approximately 1 mm tall. In some implementations, theoptics mount 305 can include two wafers: the first wafer extending thelength of the optics mount 305, and a second wafer under the region ofthe light source 315 to align the output of the light source 315 withthe axis of the lens 320. In some implementations, the first wafer canbe between approximately 0.4 mm and 0.7 mm. In some implementations, thefirst wafer can be approximately 0.5 mm tall. In some implementations,the second wafer can be between approximately 0.1 mm and 0.25 mm tall.In some implementations, the second wafer can be approximately 0.15 mmtall. The lens 320 and optical isolator 325 can extend above the heightof the first wafer of the optics mount 305. In some implementations, thelens 320 and optical isolator 325 can add between approximately 0.3 mmand 0.8 mm in height above the first wafer of the optics mount 305. Insome implementations, the lens 320 and optical isolator 325 can addapproximately 0.5 mm in height above the first wafer of the optics mount305.

In some implementations, the PIC 310 can be between approximately 0.75mm and 1.25 mm tall. In some implementations, the PIC 310 can beapproximately 1 mm tall. In some implementations, the PIC 310 can beless than or equal to 0.75 mm tall. In some implementations, the PIC 310can be between approximately 2.5 mm and 6 mm long. In someimplementations, the PIC 310 can be approximately 4 mm long. In someimplementations, the PIC 310 can be between approximately 0.75 mm and1.25 mm wide. In some implementations, the PIC 310 can be approximately1.0 mm wide. These dimensions of the components of the integratedoptical assembly 300 can allow it to fit into a typical datacommunications transceiver module.

The light source 315 can produce a continuous-wave beam of light 360with a narrow bandwidth. In some implementations, the light source 315can be a laser diode in die form. In some implementations, the diode diecan be mounted p-side down. In some implementations, the diode die canbe mounted p-side up. The light source 315 can be soldered to electricalcontacts or pads on the surface of the optics mount 305. The electricalcontacts can provide electrical current to the light source 315. In someimplementations, the light source 315 can be a distributed feedbacklaser. A distributed feedback laser is a type of laser with an activeregion that includes a diffraction grating. The grating can reflectlight at a particular wavelength to form the resonator. Distributedfeedback lasers can be susceptible to interference from external light,however. For example, any light reflected back from the optical gratingcoupler can interfere with the laser and cause it to become unstable.Therefore, in some implementations, the optics mount 305 can include anoptical isolator 325. The optical isolator 325 can pass the light beam360 in a first direction, but block any light from passing in thereverse direction back toward the light source 315. For example, theoptical isolator 325 can block light reflecting back from the interfacebetween free space and the optics mount 305, the interface between theoptics mount 305 and the PIC 310, and/or the surface of the gratingcoupler 330 and redirected by the mirror 335 back towards the lightsource 315. In some implementations, the optical isolator can be alatching garnet Faraday rotator-based micro-optical isolator.

The lens 320 can include a lens or a lens assembly for focusing thelight beam 360 onto the grating coupler 330 either directly orindirectly (via one or more reflections). The lens can be mounted on theoptics mount 305 using epoxy 350. In some implementations, the lens 320can be mounted on the optics mount 305 indirectly via one or morebrackets or mounts.

The mirror 335 redirects the light beam 360 towards the optical gratingcoupler 330. The mirror 335 includes a controllable element that canadjust the tilt or position of a reflective portion of the mirror to setthe desired angle of incidence of the light beam 360 on the opticalgrating coupler 330. In some implementations, the mirror 335 can be amicroelectromechanical system (MEMS) mirror. The mirror 335 can includeone or more actuators that can adjust the tilt or position of thereflective portion of the mirror 335 based on a supplied voltage orcurrent. In some implementations, the tilt or position of the reflectiveportion can be adjusted about one axis. In some implementations, thetilt or position of the reflective portion can be adjusted about twoorthogonal or nearly orthogonal axes. Tilting of the reflective portionmay be substantially rotational, but may also include a degree ofincidental vertical or lateral movement due to interactions betweenactuators and supporting elements. The reflective portion of the mirror335 can receive the light beam 360 via free space (i.e., air or othergas), and redirect it through the same. When the beam of light 360enters the optics mount 305, however, it can experience refraction dueto the change in refractive index. For example, the refractive index ofair is very close to 1, while the refractive index of silicon can beapproximately 3.5. In some implementations, the anti-reflective (AR)coating 340 can include one or more layers of materials with indices ofrefraction between that of silicon and air; for example, the multi-layerhard oxide coating described previously. The angle of the mirror 335 aswell as its position relative to the optical grating coupler 330 can beset to take into account this refraction and ensure the light beam 360focuses on the optical grating coupler 330. The mirror 335 is describedin more detail below with regard to FIG. 5.

The PIC 310 includes the optical grating coupler 330, which receives thelight beam 360 from the mirror 335. The PIC 310 can include a modulatorfor modulating the continuous wave light beam 360 coupled into theoptical grating coupler 330. The modulated signal can exit the PIC 310as the optical signal 365 conveying data across an optical link. The PIC310 and its components are described in detail below with regard to FIG.4.

The controller 370 can include programmable logic such as afield-programmable gate array (FPGA), a microcontroller, or amicroprocessor. The controller 370 can be integral with, or external tothe integrated optical assembly 300. The controller 370 can include amemory and interfaces for interacting with other components of theintegrated optical assembly 300. The controller 370 can includeinterfaces for receiving commands and transmitting status informationvia display, audio, input, and networking devices. The controller 370can aid in performing adjustment or calibration operations involvingpositioning of the mirror 335. In some implementations, the controller370 can include drivers (not shown) for providing analog voltage signalsto the mirror 335 for controlling the position of the reflective portionof the mirror 335. In some implementations, the drivers for providingthe analog voltage signals can be physically separate from thecontroller 370, and either adjacent to or integrated with the mirror335. In some implementations, the drivers can include digital-to-analogconvertor (DAC) for converting a digital signal from the controller 370into an analog voltage suitable for controlling the position of thereflective portion of the mirror 335. In some implementations, thedrivers can include voltage amplifiers for amplifying relativelylow-voltage (e.g., several volts) control and/or logic signals from thecontroller 370 to the relatively higher voltage (e.g., tens of volts)used to control electrostatic actuators of the mirror 335. In someimplementations, the drivers can include current amplifiers foractuating magnetic actuators. The current amplifier can convert digitalor analog voltages into currents adequate for magnetic actuation of thereflective portion of the mirror 335 (e.g., tens or hundreds ofmilliamps).

FIG. 4 is a block diagram of a photonic integrated circuit (PIC) 310 foruse in an integrated optical assembly 300, according to illustrativeimplementations. In the assembly 300, the PIC 310 can be positionedunderneath the optics mount 305. The outline 405 represents the outlineof the optics mount 305 relative to the PIC 310 in this exampleimplementation. Electrical connections are omitted for clarity.

The PIC 310 can receive the light beam 360 at the optical gratingcoupler 330. The optical grating coupler 330 couples the light beam 360into the waveguide 410. The waveguide 410 conveys the light to themodulator 415, which modulates the continuous-wave light to create andoptical signal that can be used to transmit data. The waveguide 420receives the modulated optical signal from the output of the modulator415 and conveys it to an edge coupler 425 adjacent to a side of the PIC310. The edge coupler 425 can transmit the optical signal 365 intoanother medium; for example, an optical fiber or another waveguideexternal to the PIC 310.

In some implementations, the PIC 310 can include means for measuring theamplitude of light coupled into the optical grating coupler 330. Forexample, the PIC 310 can include a monitor photodiode 430. The monitorphotodiode 430 can include a light-sensitive device such as aphotodiode, which can convert an optical signal received from a tap onthe waveguide 410 or 420 to an electrical signal that varies in relationto the amplitude of the optical signal. In some implementations, themodulator 415 can have two output waveguides. In such implementations,each output waveguide can have a separate monitor photodiode 430. Thesignals of the respective monitor photodiodes 430 can be summed. Thecontroller 370 can receive the electrical signal[s] and use it todetermine the efficiency of coupling light into the optical gratingcoupler 330. The controller 370 can further provide voltages or currentsto set a position of the mirror 335. Using the electrical signal fromthe monitor photodiode 430 as feedback, the controller 370 can adjustthe position of the mirror 335 to achieve a certain angle of incidenceof the light beam 360 on the optical grating coupler 330. The controllercan adjust mirror 335 position, and by extension the angle of incidence,to increase the efficiency of coupling light into the optical gratingcoupler 330.

In some implementations, the integrated optical assembly 300 can includea tap on the waveguide output of the modulator 415. An additionalgrating coupler or edge coupler can receive light from the tap anddirect it to an external monitor photodiode. The controller 370 canreceive an electrical signal from the external monitor photodiode anduse it to determine the efficiency of coupling of the light beam 360into the PIC 310.

In some implementations, the integrated optical assembly 300 can includeone or more additional monitor photodiodes on the optics mount 305. Thisadditional monitor photodiode can be positioned adjacent to the lightsource 315 to provide direct measurements of performance that aredecoupled from mechanical shifts of intermediary components such as thelens 320, isolator 325, and mirror 335, as well as changes in alignmentbetween the optics mount 305 and the PIC 310. These measurements can behelpful to, for example, monitor the health of the light source 315 todetect degradation of output power over time. The additional monitorphotodiode can be used in place of external monitor photodiodes duringthe burn-in manufacturing step of the optics mount 305 assembly process.

FIG. 5A is a diagram of a two-axis microelectromechanical system (MEMS)mirror assembly 500 for use in an integrated optical assembly, accordingto an illustrative implementation. The mirror assembly 500 includesthree main components: a mirror platform 505, a gimbal 510, and a mirrorsubstrate 515. The mirror platform 505, gimbal 510, and mirror substrate515 are disposed above a base substrate (not shown). The mirror platform505 can include a reflective surface and/or coating on its upper side.The mirror assembly 500 includes actuators for moving the components. Inthe implementation shown in FIG. 5A, the mirror assembly 500 can beactuated in two dimensions. The actuators 520 a and 520 b (collectively“actuators 520”) can move the mirror platform 505 with respect thegimbal 510, and the actuators 525 a and 525 b (collectively “actuators525”) can move the gimbal 510 and the mirror platform 505 with respectto the mirror substrate 515.

In some implementations, the actuators 520 and 525 can apply torque totheir inner component. For example, the actuators 520 can apply torqueto rotate the mirror platform 505 to cause rotation in the X-Z plane(i.e., about the Y-axis), and the actuators 525 can apply torque torotate the gimbal 510 to cause rotation in the Y-Z plane (i.e., aboutthe X-axis). In this manner, the actuators 520 and the actuators 525 canmove the mirror platform 505 about a first axis and a second axis,respectively, where the axes are substantially orthogonal to each other.

In some implementations, the actuators 520 and 525 can be verticalcomb-drive electrostatic actuators. Each actuator 520 and 525 can have afirst part and a second part; for example, the actuators 520 can have aleft side and a right side, and the actuators 525 can have a top sideand a bottom side, as oriented in the drawing. A first voltage appliedto the first part of the actuator can cause the actuator to move themirror platform 505 in a first direction. In some implementations, thefirst direction can be a rotational direction about an axis of motion ofthe mirror platform 505. A second voltage applied to the second part ofthe actuator can cause the actuator to move the mirror platform in asecond direction opposite the first direction. For example, the firstvoltage applied to the first part of the actuators 520 a may cause themirror platform 505 to move clockwise around the Y-axis, and the secondvoltage applied to the second part of the actuators 520 a may cause themirror platform 505 to move counterclockwise around the Y-axis.

FIG. 5B is a diagram of a single-axis microelectromechanical system(MEMS) mirror assembly 550 for use in an integrated optical assembly,according to an illustrative implementation. The mirror assembly 550includes a mirror platform 555 suspended in or over a cavity defined ina mirror substrate 565 by a torsion beam 570. The torsion beam 570allows the mirror platform 555 to move rotationally in one dimension;i.e., the Y-Z plane. The mirror platform 555 can include a reflectivelayer or surface on its top side. The mirror platform 555 can rotaterelative to the mirror substrate 565 under the influence of one or moreactuators (not shown). In some implementations, the mirror platform 555can be positioned with the aid of one or more external drivers. Anexternal driver may include an electrostatic, piezo, thermal, ormagnetic actuator. The actuators can receive a control voltage orcurrent and set a position of the mirror platform 555. In someimplementations, the mirror assembly 550 can be miniaturized. Forexample, the mirror assembly 550 can be embodied in a discrete devicehaving dimensions less than a millimeter in the x, y, and z directions.In some implementations, the mirror assembly 550 can be a discretedevice having dimensions less than 0.75 mm in the x, y, and zdirections.

In some implementations, the mirror platform 555 can be positioned viameans external to the mirror assembly 550. For example, a rod or hookcan be used to adjust the position of the mirror platform 555 whilecoupling of light into the PIC 310 is monitored. In someimplementations, the mirror platform 555 can be moved using magneticforces.

FIG. 6 is a flowchart of an example method 600 of manufacturing anintegrated optical assembly, according to an illustrativeimplementation. The method 600 includes providing an optics mount havingdisposed thereon a light source for providing a beam of light and a lensconfigured to focus the beam of light (stage 610). The method 600includes providing a photonic integrated circuit (PIC) having disposedthereon a grating coupler for receiving the beam of light and couplingthe beam of light into a waveguide (stage 620). The method 600 includesproviding a microelectromechanical systems (MEMS) mirror configured toreceive the beam of light from the lens and redirect it towards thegrating coupler (stage 630). The method 600 includes assembling theoptics mount, the MEMS mirror, and the PIC into the integrated opticalassembly (stage 640). In some implementations, the method 600 includescalibrating the position of the MEMS mirror to increase coupling of thebeam of light into the waveguide (stage 650).

The method 600 includes providing an optics mount having disposedthereon a light source for providing a beam of light and a lensconfigured to focus the beam of light (stage 610). The optics mount canbe similar to the optics mount 305 described with respect to FIG. 3.Likewise, the light source can be similar to the light source 315, andthe lens can be similar to the lens 320. The light source 315 can bebonded or otherwise mounted to the optics mount 305 using a solder 345or adhesive. The lens 320 can be fixed to the optics mount 305 via acombination of an adhesive and/or a bracket or mount. The light source315 and lens 320 are arranged such that the light source 315 can directa beam of light towards the lens 320.

The method 600 includes providing a photonic integrated circuit (PIC)having disposed thereon a grating coupler for receiving the beam oflight and coupling the beam of light into a waveguide (stage 620). ThePIC can be similar to the PIC 310 described with respect to FIGS. 3 and4. Likewise, the grating coupler can be similar to the optical gratingcoupler 330.

The method 600 includes providing a microelectromechanical systems(MEMS) mirror configured to receive the beam of light from the lens andredirect it towards the grating coupler (stage 630). The mirror can besimilar to the mirror 335 described with respect to FIG. 3, includingthe mirror assemblies 500 and 550 described with respect to FIG. 5. Themirror 335 can be mounted or attached to the optics mount 305. In someimplementations, the mirror 500 or 550 can include one or more actuatorsfor adjusting a position of the MEMS mirror to affect an angle ofincidence of the beam of light on the grating coupler 330.

The method 600 includes assembling the optics mount, the MEMS mirror,and the PIC into the integrated optical assembly (stage 640). The opticsmount 305 and the PIC 310 can be joined and bonded using an adhesivesuch as epoxy or solder balls applied via a solder shooter, or bymechanical fasteners such as bolts or clamps. The mirror 335 can bejoined to the optics mount 305 and/or the PIC 310. The mirror 335 can befixed in position such that it can receive the light beam 360 from thelight source 315 and lens, and redirect the light beam 360 through theoptics mount 305 to the optical grating coupler 330 on the PIC 310.During the assembly stage, it is important to properly align the opticsmount 305 and the PIC 310 in the X-Y plane to achieve alignment betweenthe light beam 360 and the optical grating coupler 330, which may be assmall as several microns in each dimension. In some implementations, afocused spot size of the light beam 360 can be approximately 10 μm indiameter. In some implementations, alignment may be performed visuallyby activating the light source 315 and observing the point of incidenceof the light beam 360. In some implementations, alignment may beperformed using feedback from the monitor photodiode 430 to measureoptical coupling.

In some implementations, the method 600 includes calibrating theposition of the MEMS mirror to increase coupling of the beam of lightinto the waveguide (stage 650). In some implementations, the lightsource 315 can be activated, and the mirror 335 adjusted to direct thelight beam 360 onto the optical grating coupler 330. A position and/ortilt of a reflective portion of the mirror 335 can be adjusted to set anangle of incidence of the light beam 360 on the optical grating coupler330. The angle of incidence can be adjusted to increase coupling of thelight beam 360 into the grating coupler 330.

While this specification contains many specific implementation details,these should not be construed as limitations on the scope of anyinventions or of what may be claimed, but rather as descriptions offeatures specific to particular implementations of particularinventions. Certain features that are described in this specification inthe context of separate implementations can also be implemented incombination in a single implementation. Conversely, various featuresthat are described in the context of a single implementation can also beimplemented in multiple implementations separately or in any suitablesub-combination. Moreover, although features may be described above asacting in certain combinations and even initially claimed as such, oneor more features from a claimed combination can in some cases be excisedfrom the combination, and the claimed combination may be directed to asub-combination or variation of a sub-combination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. In certain circumstances, multitasking and parallel processingmay be advantageous. Moreover, the separation of various systemcomponents in the implementations described above should not beunderstood as requiring such separation in all implementations, and itshould be understood that the described program components and systemscan generally be integrated together in a single software product orpackaged into multiple software products.

References to “or” may be construed as inclusive so that any termsdescribed using “or” may indicate any of a single, more than one, andall of the described terms. The labels “first,” “second,” “third,” andso forth are not necessarily meant to indicate an ordering and aregenerally used merely to distinguish between like or similar items orelements.

Various modifications to the implementations described in thisdisclosure may be readily apparent to those skilled in the art, and thegeneric principles defined herein may be applied to otherimplementations without departing from the spirit or scope of thisdisclosure. Thus, the claims are not intended to be limited to theimplementations shown herein, but are to be accorded the widest scopeconsistent with this disclosure, the principles and the novel featuresdisclosed herein.

What is claimed is:
 1. An integrated optical assembly comprising: anoptics mount having disposed thereon a light source for providing a beamof light and a lens configured to focus the beam of light; a photonicintegrated circuit (PIC) mechanically coupled to the optics mount andhaving disposed thereon a grating coupler for receiving the beam oflight and coupling the beam of light into a waveguide; and amicroelectromechanical systems (MEMS) mirror configured to receive thebeam of light from the lens and redirect it towards the grating coupler,wherein a position of a reflective portion of the MEMS mirror isadjustable to affect an angle of incidence of the beam of light on thegrating coupler.
 2. The integrated optical assembly of claim 1, whereinthe grating coupler includes silicon.
 3. The integrated optical assemblyof claim 1, wherein the optics mount includes silicon with ananti-reflective coating on at least one surface.
 4. The integratedoptical assembly of claim 1, wherein the light source is a distributedfeedback laser.
 5. The integrated optical assembly of claim 4,comprising: an optical isolator disposed on the optics mount andconfigured to receive the beam of light from the lens and pass it in afirst direction towards the MEMS mirror while preventing light frompassing through it in a second direction opposite the first direction.6. The integrated optical assembly of claim 1, comprising: a monitorphotodiode disposed on the PIC for measuring an amplitude of lightcoupled into the waveguide.
 7. The integrated optical assembly of claim1, wherein the MEMS mirror is movable to adjust the angle of incidencefrom zero degrees from normal to a light-receiving surface of thegrating coupler, to 20 degrees from normal.
 8. The integrated opticalassembly of claim 1, wherein the optics mount is less than 5 mm long,1.25 mm wide, and 1.5 mm tall, and the PIC is less than 1.25 mm tall,1.25 mm wide, and 6 mm long.
 9. The integrated optical assembly of claim1, wherein the MEMS mirror can rotate in two dimensions.
 10. Theintegrated optical assembly of claim 1, wherein the MEMS mirror includesan actuator for adjusting the position of the reflective portion. 11.The integrated optical assembly of claim 1, wherein the MEMS mirror isconfigured to be continually or periodically repositioned throughout aservice life of the integrated optical assembly.
 12. An opticalcommunication system comprising: an optics mount having disposed thereona light source for providing beam of light and a lens configured tofocus the beam of light; a photonic integrated circuit (PIC)mechanically coupled to the optics mount and having disposed thereon: agrating coupler for receiving the beam of light and coupling the beam oflight into a waveguide, and a monitor photodiode for measuring anamplitude of light coupled into the waveguide; a microelectromechanicalsystems (MEMS) mirror configured to receive the beam of light from thelens and redirect it towards the grating coupler, wherein a position ofa reflective portion of the MEMS mirror is adjustable to affect an angleof incidence of the beam of light on the grating coupler; and acontroller configured to receive an indication of the amplitude of thelight coupled into the waveguide and control the position of the MEMSmirror to increase the indication of the amplitude.
 13. The integratedoptical assembly of claim 12, wherein the grating coupler includessilicon.
 14. The integrated optical assembly of claim 12, wherein theoptics mount includes silicon with an anti-reflective coating on atleast one surface.
 15. The integrated optical assembly of claim 12,wherein the light source is a distributed feedback laser.
 16. Theintegrated optical assembly of claim 16, comprising: an optical isolatordisposed on the optics mount and configured to receive the beam of lightfrom the lens and pass it in a first direction towards the MEMS mirrorwhile preventing light from passing through it in a second directionopposite the first direction.
 17. A method of manufacturing anintegrated optical assembly comprising: providing an optics mount havingdisposed thereon a light source for providing beam of light and a lensconfigured to focus the beam of light; providing a photonic integratedcircuit (PIC) having disposed thereon a grating coupler for receivingthe beam of light and coupling the beam of light into a waveguide; andproviding a microelectromechanical systems (MEMS) mirror configured toreceive the beam of light from the lens and redirect it towards thegrating coupler, wherein a position of a reflective portion of the MEMSmirror is adjustable to affect an angle of incidence of the beam oflight on the grating coupler; and assembling the optics mount, the MEMSmirror, and the PIC into the integrated optical assembly.
 18. The methodof claim 17, comprising: providing a modulator on the PIC for modulatinglight coupled into the waveguide.
 19. The method of claim 17,comprising: providing a monitor photodiode on the PIC; and measuring,using the monitor photodiode, an amplitude of light coupled into thewaveguide.
 20. The method of claim 19, comprising: calibrating, usingthe measured amplitude, the position of the MEMS mirror to increasecoupling of the beam of light into the waveguide.